Filtering apparatus and method



May 30, 1944. c. E. FRASER FILTERING APPARATUS AND METHOD Filed June 7,1940 2 sheets-sheep 1 T If B ATTORNEY.

May 30, 1944.

. C. E. FRASER FILTERING APPARATUS AND METHOD 2 Sheets-Sheet 2 FiledJune 7, 1940 ATTORNEY.

Patented May 30, 1944 UNITED STATES PATENT omcs 9 Claims.

The present invention relates to a method of and mechanism for cleaningfilter beds.

It is common practice in the treatment of sewage, industrial wastes,etc. to pass liquids containing the same through relatively shallow bedsof sand, aggregate or the like, which removes the sol-ids therefrom.Such beds, in the course of time, become clogged with the retainedmaterial, even though the raw material undergoing treatment has beensubjected to preliminary treatment such as sedimentation or the like. Asa consequence, it becomes necessary to restore the bed to somewhere nearits initial solid removal capacity and this may be done by cleaning iteither intermittently orcontin'uously.

A popular type of cleaning mechanism for the above purpose consists of atravelling cleaner operated above the bed, which includes a cleanercaisson. The caisson is intended to make a sealing contact with theportion of the bedimmediately thereunder and this is accomplishedusually by extending the side walls of the caisson into the bed materiala sufficient distance and by providing sealing means, such as hollow,rotating drums at each end of the caisson and sliding contact along thesides. Consequently, the small portion of the bed-which is being cleanedis temporarilycompletely cut off from a filtering action:

The cleaner caisson may be divided into two compartments, in the firstof which the filter bedmaterial is agitated and the retained solidsloosened therefrom, the wash Water resulting from such action passingover into the second or wash'water compartment from which it is removedby a pump for disposal or further treatment;

' The above mechanism is applicable both to upflowanddownfiow filters.

In downflowfilters, it is customary to flow the unfiltered infiu'ent,with or without previous treatment, such as sedimentation; directly ontopof the filter bed, the liquid passing through the bed; the solidsbeing caught thereby and clean efiluent resulting. This'efiluent thenmoves from beneaththe bed and into a disposal channel, the

level of which is maintained slightly below the from time to time due tothe quantum ofretained solids therein, means" are provided for varyingthe hydraulic head between the influent and eflluent levels. Thisusually consists in arrang ing the parts so that the influe'nt Willautomatisally build up to a-hi'glier levelfithan that of the effiuent.Thi may conveniently take the form of an adjustable weir'on the effluentdischarge. This weir may be automatically operated within a narrowrange, by a, float" on the" in'ilu'ent side of the filter.

A convenient method of agitating a portion of the filter bed to cleanthe same may take the form of an intermittently operated solenoid wherethe bed material is or the magnetite sand variety. This electromagnet',submerge in the liquid, being located relatively close to the bed; whenenergized for't'he space of about a second,- lifts a section of themagnetite sand immediately thereunderand this movement and the subs=quent dropping of the sand back into the bed, tends to separate thesolids caught by the sand therefrom. Inasmuch. as the lifting of thismagnetite creates azone of lessened resistance in the bed at that point,if, as in a dcwnflow filter,- the eflluent level ishigher than the Washwater level in the solenoid compartment in the caisson, there will be aback rush or cleaneflluent up through the bed at the area of lessenedresistance, Whichwas'hes thel'oosened solids from the magnetite, overthe partition betweenthe agita: tion compartment and wash water and intothe latter from which it; is IeniOV'ed by a} pump. This cleaningprocedure may take place continu ously. V

Other mechanism for creating the area of agi tation: in the bed other anelectromagnet may consist of pipes projecting a suitable distance intothe material eitherto simply are sure the bed or this disturbance may befacili tated by injecting air or other liquidtlirough-the' pipes. 'Thesemethod's of agitation are also able for a bed of sand or other aggregatenot of the magnetitevariety.

In upfiow filters, much the same procedure takes place althoughin thatcasegtliia influe'nt to be filtered flows nom beneatnme bed, upthroughthe bed material, theciean effluent being Oil top" thereof; As beiore,theini'luent level must is above that of the eliiueiit in ordertdinducet' s hydraulic now. Likewise, the*cleaner mechanism creates anarea ofagitatitin inthe'bed but in this case, the flood or watersnroirgn the area or lessened resistancecaused thereb is that ofunfiltered; influe'rit from below thebed; thus carry ing the loos'eneddirt over the wash water weir and int'othe' wash water box where'- itis-removed bya pump; i

In both cases, it meta-noted that the cleaner caisson defines an area ofresistaneeagamst the new of liquid therethrough-and iscutofffromtlieliquid surrounding it by the seals which exist at the side andends thereof and that consequently, no filtering action takes place inthe area covered by the cleaning mechanism.

The main function of the seals is to assist the wash water pump tocreate a back head and prevent the wash water from contaminating theeffiuent. In the case of downfiow filters, the seals also prevent theunfiltered infiuent from above the bed leaking into the cleaner caissonand from thence through the bed-at its area of lessened resistance tothus contaminate the clean eifiuent below. In the case of upfiowfilters, the seal prevents the rush of unfiltered infiuent movin upthrough the area of lessened resistance in the bed from leakingoutwardly through the cleaner caisson to contaminate the clean efiluentabove the bed. i

Actual operations in the field of downfiow filters have indicatedcertain limitations such as the fact that for hydraulic reasons, it isimpracticable to deliver to thesurface ofthe bed more than acertainmaximum of sewage per square foot of bed per minute, no matter how smallthe suspended solids content of the sewage may be. This maximum is,therefore, thepeak load of the filter bed and the normal rate mustconsequently be considerably less. The limitation of capacity of upfiowfilters is even more severefor other reasons, as an excessiverate ofvupfiow lifts the filtering aggregate en masse instead of flowingsmoothly through the interstices.

Again, it hasbeen foundimpracticable to operate a submergedcleanerfaster than at a certain speed, This is due to the fact that ifthe cleaner mechanism-moves fasterthan this maximum, it pushes a wall ofsettled sewage from the top of the ,bed ahead of it, themovement ofwhich has a tendency to erodefthe surface of the bed material itself.This disturbance, added to the other hydraulicj disturbances of the bedmaterial, is something to be avoided.

,Inasmuch as these cleaning devices may not operate as fast as would bedesirable under the circumstances, it follows. either that the flow ofinfiuent must bereduced, additional cleaner must be providedor-.-additional sewage systems or filters installed. I

It is the principal object of the present inven-. tion, therefore, toprovide means whereby the efficiency of these cleaning devices may bestepped up to the point thatthebeds have increased ca pacity and,consequently, can take care of greater fiow of infiuent containing agreater quantity of solids than would be possible heretofore, allwithout increasing the size or number of the cleaning mechanismsthemselves and while re-. taining the beds in their normal area and atuniform level and thickness. r.

It has been found that the choking of adownflow filter bed is dueprimarily to the retaining of solids at the surface with which theinfiuent first contacts. That is, the retained solids are not equallydistributed throughout the bed :material, but onthecontrary, formarather thin film or skin on the bed whilethe remainderof the bedthickness remains reasonably clean. Under such circumstances, it onlybecomes necessary to break up this surface film or skin-whereupon thebed is restored to nearly its normal capacity. 'As a consequence, thisskin or film breaking procedure supplements the cleaning mechanismandmakes it unnecessary for the cleaner to pass over the, bed to completelyclean the sameas often as would be otherwise required. Of course, thissurface operation is useful only as a temporary ex pedient, foreventually the deep cleaner such as above described must be used tocleanse the bed material all the way down to the wire on which it issupported.

It has been found that the normal condition of settled solids upon thesurface of a bed and immediately thereunder is that such solids exist aslight, fiufiy solids only slightly greater in specific gravity than thefiuid from which they have been settled. Consequently, such settledsolids are easily disturbed and redisseminated through the influent.Therefore, the usual sealing means provided for blocking off an area ofthe bed during the cleaning operation has a tendency to push ahead of ita wall of, and disturb, the solids in the path of the cleaningmechanism. It has also been found that due to this lack of adhesionand/or cohesion between the solid particles, that in the bed washingapparatus or zone of agitation, they are so completely disseminated asvery fine particles that it is most difficult to again settle them outsubsequent to removal from the bed. It has been discovered, however,that if these settled solids caught by the area of the bed to be cleanedcan be coagulated or fiocculated, that thereafter the fiocs or clumps ofsolids may not only be more readilywashed from the bed in comparativelylarge masses without undue dissemination but that they may besubsequently satisfactorily settled from the wash water.

It will be apparent that any kind of sealing mechanism used inconjunction with a travelling cleaner device has a tendency to disturbthe bed at the point of contact and consequently tends to permit leakageof the caught, fine solids through the bed into the clean eflluenttherebelow. This detrimental action may be prevented by the use ofsealing means which at the same time causes a compression of the beditself. This has the effect of reducing the size of the intersticesexisting between the particles of the bed material, thus making the bedas a whole more dense. Consequently, there is less liability for thepassage of fine particles through the bed at this point into theefiluent.

To this end, the invention in one of its aspects contemplates theprovision of means travelling ahead of the cleaner which will not onlycompress the layer of light, settled solids on top of and immediatelybeneath the bed into a more or lessdense and compact mass orfilm butwill at the same time, compress the bed material itself at this point.If this film or compressed mass of solids is then subjected to agitationeither in the form of a zone immediately beneath a cleaning mechanism orby means of rakes preceding the cleaner mechanism where the rakes extendonly into the compressed area, relatively large flocs of solids areformed which are much more easily re-. moved by the washing apparatusand much more easily settled from the wash water therafter.

Again the invention contemplates the use of an additional rakeimmediately following in the path of the cleaner apparatus which willhave a I tendency to restore the level and surface continlar and annularvarieties, in the former of which the cleaning mechanism moves back andforth over the bed while in the latter the apparatus moves round andround, usually in one direction.

The invention further consists in the novel arrangement, combination andconstruction of parts more fully hereinafter shown in the drawings, inwhich- I Fig. 1 is a side elevation partly in section of an apparatusembodying the present invention;

Fig, 2 is an enlarged detail of an agitation creating means togetherwith the rakes movable ahead of and behind the agitation means;

, Fig. 3 is a fragmentary front view of one form of rake;

Fig. 4 is a fragmentary sectional enlarged view showing the manner ofattachment of a rake to a cleaner caisson;

' Fig. 5 is a fragmentary sideelevation of one form of compression meansshowing its action on the settled solids and bed;

Fig. 6 is a view similar to Fig. 5 showing the compression means ashaving moved forward over the bed a limited extent from the position ofFig. 5.

Referring now to Fig. 1, the usual filter bed is shown at I of sand,such as that of the magnetite or silica variety or any other aggregateor filter media. A suitable thickness of bed material rests upon ascreen 2 supported by grid 3 resting upon the top of wall 4 so as toslightly space the grid from the bottom 5 of the filter tank. The space6 serves as an effluent channel for the clean filtered material.

Influent to be filtered either with or without preliminary treatmentsuch as sedimentation or the like is flowed on top of the bed I until asuitable level I above the adjustable effluent level E has been reached.This hydraulic head causes movement of the liquid to be filtered throughthe bed I, the latter retaining the solids so that the clean effluentflows into the space 6 beneath the bed. The clean efiluent then passesupwardly through a vertical channel and spills over an adjustable weir lwhich establishes the effluent level E lower than the influent level 1.Adjustment of the weir I may be made at will and by any suitable meansnot shown to determine the relationship between these levels.

A suitable cleaning mechanism. may consist of a trolley movable by motor8 through wheels 53 mounted on a trackway I0. Depending from the trolleyis a caisson consisting of a front wall II, a rear wall I2 and sidewalls I3. A partition i4 divides the. caisson into an agitationcompartment I5 and a wash water compartment I6. In the former is asolenoid I! or other agitation causing means while in the latter a pumpI8 is located for removing wash water therefrom.

The caisson makes a sealing contact with the filter bed for the purposeabove described and this may be accomplished at the sides by extendingthe side walls I3 into the bed material a sufficient distance, and ateach end through the instrumentality of forward roller I9 and rearroller 28 suitably carried in the side walls I3 and making a water-tightsliding connection therewith. The rollers are provided with a series ofcleats 2| on the periphery thereof not only to facilitate a sealingcontact with the bed but for the purpose of trapping the forward movingwave of bed material and settled solids.

The solenoid I! may be connected to a suitable intermittent source ofelectrical energy so as to energize the same. Upon establishing thisconnection, where the sand of the filter bed is of the magnetitevariety, the latter is magnetized and an area thereof bodily lifted uptoward the solenoid, which loosens the dirt adherent to the sand. It isto be noted that by suitable adjustment of the relative height of thesolenoid or the degree of magnetic force created therein, any amount ofbed may be lifted from 'a small amount to one completely down to thewire.

Assuming that a section of the bed down to the wire is lifted, thiscauses an area of agitation and weakened resistance in the bed and dueto the fact that the wash water level W in the wash water caissonestablished by reason of adjustable weir 22 in intermediate wall I4 islower than that of the effluent level E, clean effluent from below thebed flows up through thisarea of lessened resistance, washes the dirtloosened from the sand and spills the thus produced wash water over thetop of weir 22 into the wash water compartment I6 from which it isremoved by the pump I8. When the solenoid I"! is de-energized, itreleases the magnetite which drops back into the bed substantiallyclean. The deep cleaning operation then repeated intermittently untilthe entire area of the bed has been subjected to the purging action.

t will be observed that by the use of a roller of suitable weighttravelling ahead of the cleaning mechanism as particularly shown in Fig.5, there will be a tendency for a wave 23 of bed material and a wave 24of settled solids to move ahead of the roller. Unless means are providedto prevent this action, not only does the bed material gradually thinout in the center of rectangular beds but it is caused to build up to anundue extent at the ends thereof. MoreoverQthe wave 24 of settled solidsbeing comparatively light and uncompacted will be disturbed anddisseminated throughout the infiuent liquid so that they cannot beefficiently removed in the subsequent cleaning operation.

As shown in Fig. 5, the cleat 2| moves down ahead of the advancing wallsof sand 23 and solids 24, traps them as in Fig. 6 and finally compressesthe solids into a compact layer 25 while at the same time leaving thesand at a level 26, lower than that of its level 2'! prior topassage ofthe roller I 9. In this compression period, some of the loose solids ontop of the bed have been pushed into, and below the surface of, the'sandso that with the exception of the compressed film 25, the majority ofsolids are included in the top portion of the bed.

Not only does the cleat action prevent the segregation of bed materialby trapping the mov ing Wave thereof but it also avoids the disturbanceof the settled solids by passage of the roller thereover.

Referring back to Figs. 1, 2 and 3, it will be observed that as thecleaner progresses in the path of the roller I9, a rake 23 carried bysupport 29 which is mounted for adjustable vertical,

movement by means of the handwheel 3i! breaks up the compacted layer ofsolids 25 by means of its teeth 3|. This causes the formation of flocs32 as well as plows the upper one-third of the bed carrying the majorityof compacted bed material and solids. When, therefore, the sclenoid H isenergized, the loosened bed material is lifted from the screen 2 and theupflowing clean effluent from below carries the flocs and their dirtover the top of weir 22 into the wash water compartment I 6 from whichit may be removed.

After the solenoid has become deenergized so as to drop the magnetiteback into its place on the screen 2, any unevenness in the surfacethereof is leveled out by means of the teeth of rake 33 attached to thewall M. It is preferable to stagger theteeth in rakes 28 and 33.

While the above operation has been described with relation to movementof the cleaning device in one direction, yet its operation is similarwhen moved in the opposite direction.

As a result of the above instrumentalities a much more efficientcleaning operation is obtainable than has been possible heretofore, dueprimarily to the formation of a compacted layer of solids and bed. Thisis ,a much more advantageous operation than has been heretoforeaccomplished, where, for instance, sliding shoes and buoyant drums havebeen used either to make a sealing contact with the sand or to supportthe movable cleaner mechanisms. Unless there is a definite deliberateweight placed upon the bed, compression of the surface and adjacentsolids and bed cannot be accomplished.

I claim:

1. A method of cleaning a downflow filter bed which includes segregatingan area of the bed, compacting the solids caught by the upper portion ofthe bed, as the filtrant flows downwardly through it, in the segregatedarea substantially completely across the bed while at the same timecompacting the bed itself so that the solids are pressed into the bedand compacted onto the bed in a dense film, thereafter raking the uppercompacted surface only of the compacted area of the bed and subsequentlylifting portions of the bed which have been raked in said segregatedarea and washing out and removing the solids therefrom.

2. A method of cleaning a downflow filter bed which includes segregatingan area of the bed, compacting the solids caught by the upper portion ofthe bed, as the filtrant flows downwardly through it, in the segregatedarea substantially completely across the bed while at the same timecompacting the bed itself, so that the solids are pressed into the bedand compacted onto the bed in a dense film, thereafter raking the uppercompacted layer only of the bed to break the compacted solids into flocsand subsequently creating a zone of agitation in the fiocced segregatedarea of the bed which has been raked and washing out andremoving thesolids therefrom.

3. A method of cleaning a downflow filter bed which includes segregatingan area of the bed;

. compacting solids caught by the upper portion of the bed, as thefiltrant flows downwardly through it, in the segregated areasubstantially completely across the bed while at the same timecompacting the bed itself so that the solids are pressed into andcompacted onto the bed in a dense film, raking the upper one-thirdthickness only of the compacted bed to form flocs, there after liftingportions of the flocced segregated area of the bed which has been rakedand washing out and removing the solids therefrom.

4. A method of cleaning a downfiow filter bed in which the filtrantflows downwardly through it, which includes segregating an area of thebed, compacting the solids caught by the upper portion of the bed, asthe filtrant flows downwardly through it, in an area substantiallycompletely across the bed while at the same time compacting the beditself, so that the solids are pressed into and compacted onto the bedin a dense film, raking the upper compacted surface only of thecompacted bed, thereafter lifting portions of the raked segregated areaof the bed and washing out and removing the solids therefrom.

5. In combination, travelling means extending substantially completelyacross a filter bed and in contact therewith to compact the bed and thesolids caught by the upper portion thereof, a rake extending downwardlythrough the compacted bed area only traveling behind and in the path ofthe compacting means to break up the compacted solids into flocs, meansto create a zone of agitation in and beneath the fiocced area of thebed, which has been raked, by raising portion thereof, and means forwashing out and removing the solids from the said zone.

6. The combination of claim 5 in which the compacting means is a roller.

7. The combination of claim 5 in which the compacting means is a cleatedroller.

8. The combination of claim 5 with an additional rake travelling behindthe zone of agitation to level the bed.

9. A method of cleaning a downflow filter bed which includes segregatingan area of the bed, compacting the solids caught by the upper portion ofthe bed, as the filtrant flows downwardly through it, in the segregatedarea substantially completely across the bed while at the same timecompacting the bed itself, so that the solids are pressed into the bedand compacted onto the bed in a dense film, thereafter raking the uppercompacted layer only of the bed to break the compacted solids into fiocsand subsequently creating a zone of agitation, extending completely tothe bottom of the bed, in the fiocced segregated area of the bed whichhas been raked and washing out and removing the solids therefrom.

CHARLES E. FRASER.

